Method for charging and discharging lithium secondary battery, and system for charging and discharging lithium secondary battery

Abstract

A charge / discharge method for a lithium secondary battery is performed on a lithium secondary battery including a positive electrode containing a positive electrode active material capable of occluding / releasing lithium ions; a negative electrode containing a negative electrode active material capable of occluding / releasing lithium ions; a separator located between the positive electrode and the negative electrode; and an electrolyte having a lithium ion conductivity. The positive electrode active material contains a lithium-containing transition metal oxide; and a reversible capacity of the negative electrode is larger than a usable capacity of the positive electrode. First charge / discharge is performed by which the positive electrode in a charged state is discharged until having a first potential VDp1, which is lower than 2.7 V on a lithium metal basis, and the discharge is finished at this point.

Description

TECHNICAL FIELD[0001]The present invention relates to a charge / discharge method and a charge / discharge system for a lithium secondary battery.BACKGROUND ART[0002]Lithium secondary batteries have a large capacity and a high energy density and are easy to be decreased in size and weight, and therefore are widely used as power supplies of small-sized mobile electronic devices, for example, mobile phones, personal digital assistants (PDAs), laptop personal computers, camcorders, portable game machines and the like. In the future, such small-sized mobile electronic devices are desired to have a larger number of functions and to be drivable for a longer time.[0003]In order to attain a further increase in the capacity of lithium secondary batteries, development of active materials is under way. As positive electrode active materials, lithium-containing transition metal oxides, for example, are used. Known lithium-containing transition metal oxides include lithium-containing complex oxides ...

AI Technical Summary

Benefits of technology

The present invention relates to a method for charging and discharging a lithium secondary battery. The method prevents deterioration of the negative electrode and maintains the initial battery capacity, even after repetitive charge / discharge cycles. This is achieved by setting the discharge end potential of the positive electrode to a potential lower than 2.7 V, which can utilize the deterioration specific to the negative electrode caused by the repetition of charging and discharging cycles. The negative electrode is prevented from being deteriorated by the long-term repetition of charging and discharging cycles, resulting in a suppression of decrease in battery capacity.

Problems solved by technology

However, there is a problem that a lithium secondary battery using LiNiO2 has a short charge / discharge cycle life due to the low stability of the crystalline structure of LiNiO2.

These materials occlude / release a large amount of lithium.

When this occurs, electron conductivity is not provided, which may undesirably decrease the capacity and also cause lithium metal to be deposited on the current collector.

However, when the amount of lithium to be occluded / released to / from the positive electrode active material is decreased, neither the capacity nor the long-term cycle life can be improved although a certain effect of improving the reversibility is provided.

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